Advanced motor controller

Abstract

A controller for close positioning or modulating control of an electric motor is disclosed. The controller compares a signal representative of the demand on the system with a signal representative of the actual position of the motor or a valve associated therewith, and if the difference between the signals exceeds a "deadband" and no action has been taken within a first time interval, and if the last movement of the valve was in the same direction and a second time interval has elapsed, a motor run pulse is generated. If the last movement of the valve was in a direction opposite to that desired, the motor run pulse is extended to overcome "backlash" resulting from the reversal of motor rotation.

We claim: 
     
       1. A control device for close positioning or modulating control of a positioning device comprising means for comparing the actual position of the positioning device with the desired position of the positioning device, said comparing means producing an output signal when said actual position of the positioning device differs from said desired position of the positioning device by more than a predetermined value, and means responsive to said output signal produced by said comparing means, said output signal responsive means causing the positioning device to move toward said desired position if a first predetermined period of time has elapsed since the last movement of the positioning device and if a second predetermined period of time has elapsed if the last movement of the positioning device was in a direction opposite to that of said desired position of the positioning device, said output signal responsive means including means for increasing the period of time the positioning device is actuated if the last movement of the positioning device was in a direction opposite to that of said desired position of the positioning device. 
     
     
       2. The control device as defined in claim 1 wherein said output signal responsive means further includes means for actuating the positioning device for a minimum period of time, said minimum time period actuating means being operable upon the initiation of each output signal produced by said comparing means. 
     
     
       3. The control device as defined in claim 1 further including means for determining movement of the positioning device after said output signal from said comparing means has ceased, said movement determining means preventing further movement of the positioning device until said first predetermined period of time has elapsed. 
     
     
       4. The control device as defined in claim 1 further including means for overriding said output signal responsive means permitting the closing of the positioning device. 
     
     
       5. The control device as defined in claim 1 further including means for determining the rate of change of the position of the positioning device, said rate of change determining means preventing further movement of said positioning device for said first predetermined period of time if the rate of change of the position of the positioning device exceeds a predetermined level.